Several alternatives have been proposed, which based on hydraulic pressures or mechanic actuators, modify the entire piston height or a part of it, but they are not able to react synchronically with the high speed of the changing pressures in the combustion chamber.
Given that those mechanisms are not directly connected to the pressures in the combustion chamber, they have an important delay in reference to the speed of change of the combustion chamber pressures which change at the piston speed, within the range of several thousand revolutions per minute that the engine works.
An additional problem arises with the alternatives that separate the piston crown by hydraulic mechanisms or mechanic actuators and also if a spring would be used, and it's that the piston crown would be under lateral forces generated by the pressures on the piston head against the resistance of the connecting rod to the crankshaft, which works inclining itself according to the crankshaft rotation. Those lateral forces would produce a high frequency desalignments among the skirts of the piston crown and that of the piston trunk.
That desalignment vibration would affect the coupling mechanism for the piston crown and the piston trunk, which are designed for vertical displacements only, so it's structural stability would be compromised.
Another important problem associated to those alternatives that separates the piston crown from the piston trunk, is that because the crown is the more massive part of the piston and it's inertia produces big impacts to stop it's movement at the top end and also at the bottom end against the trunk part.
The present invention permits a gradual adjustment of the compression ratio depending directly on the different pressures over the piston head, generated by the different fuel gas loads, in the combustion chamber, along the entire range of revolutions per minute of the engine work. More over, this invention doesn't have the problems mentioned before associated to the other alternatives.